FIG. 5 is a cross section of an inside of the gas turbine. The gas turbine is used for the convenience of explanation of the present invention, and does not belong to the category so-called known art. In FIG. 5, a first blade ring 31 and a second blade ring 32 are separated. The first blade ring 31 and the second blade ring 32 correspond to a first moving blade 33 and a second moving blade 34, respectively. Circumferential blade ring cooling passages 35 and 36 are provided inside the first blade ring 31 and the second blade ring 32 respectively. The cooling passages 35 and 36 are axially connected with each other through a communication pipe 37.
From the outside of the blade rings 31 and 32 (herein, the outside of a wheel chamber 38) cooling air 39 to cool down stationary blades is forcefully introduced. The cooling air 39 flows through a space made by an inner wall of the wheel chamber 38 and outer surfaces of the blade rings 31 and 32, and eventually flows into the inside of a stationary blade 40, then is exhausted from small holes 41 provided on the surface of the stationary blades.
Temperature and pressure-controlled steam flows inside the cooling passages 35 and 36. Thereby, the steam optimally maintains clearance between the first moving blade 33 and an inner wall 42 of the first blade ring that opposes the blade 33, and also the clearance between the second moving blade 34 and an inner wall 43 of the second blade ring that opposes the blade 34, while the turbine is running. Meanwhile, if the cooling air 39 hits outer surfaces of the blade rings 31, 32, and the communication pipe 37, due to an effect of heat transfer, the cooling air 39 affects the temperature of the steam flowing inside the cooling passages 35 and 36, because the temperature of the cooling air 39 is different from the temperature of the steam. Thermal shields 44 are provided on the outer surfaces of the blade rings 31, 32, and the communication pipe 37, to avoid direct contact of the cooling air 39 with the outer surfaces of the blade rings 31, 32, and the communication pipe 37.
It is not appropriate to attach the thermal shields 44 directly to the blade rings 31 and 32, because the thermal shields 44 are made of metal plates, and have a different thermal expansion coefficient from a thermal expansion coefficient of the blade rings 31 and 32 at the same temperature. Thus, the thermal shields 44 are bolted to the outer surfaces of the blade rings 31 and 32 through spacers. By this means, gaps are produced between the outer surfaces of the blade rings 31 and 32 and the thermal shields 44. According to the art, a thermal shield effectiveness of the thermal shields 44, and the air existing in the gaps, enhanced the effects of the thermal shields.
However, according to the art, there are slight gaps between the outer surfaces of the blade rings and the thermal shields. Therefore, by forced convection (especially, by dynamic pressure) of the cooling air which is high-speed and high-pressure, the air with a different temperature from the steam temperature, easily and problematically enters into the gaps. If the high-speed air enters into the gaps, a heat transfer coefficient of the outer surface of the blade rings and the like fluctuates, thereby the effect of the thermal shields reduces by half.
Therefore, it is an object of the present invention to provide a gas turbine that effectively controls a loss of heat in the blade ring cooling passages by adding a contrivance to the gaps between the outer surfaces of the blade rings and thermal shields.